chosen were XI PM-3 as the experimental group and XI PM-2 as the control group.
4.2.4 The Results of Try out Test for Vocabulary Post Test
The results of try out test, in this research, including the analysis of test validity, difficulty index and reliability coefficient were presented respectively.
4.2.4.1 The Analysis of Test Validity
Regarding to the validity of the test, this research used content validity because it was constructed based on the material stated in the institutional based
curriculum and competence standard used for teaching English and the indicators to be measured. Based on the reason, it could be said that the test fulfilled the
requirement of content validity. Besides, the test items were consulted to both of the advisers and to the English teacher of SMKN 1 Jember.
4.2.4.2 The Analysis of Difficulty Index
The try out for vocabulary post test was given to one class of the existing three classes of the eleventh grade PM Marketing which was not selected as the
experimental group and the control group. After doing the try out, the researcher started to analyze the difficulty index. From the result, the value of each items
indicated that the test was fair or enough. The difficulty index for all test items were concluded as good because the difficulty index was neither too easy nor too
difficult. The analysis of difficulty index of try out for vocabulary post test in detail can be seen on Appendix G.
4.2.4.3 The Analysis of Reliability Coefficient
In this research, to know the value of the reliability coefficient, split half odd-even technique using the computation of Microsoft Excel was applied in this
research. The researcher signed X for the odd numbers and Y for the even numbers. Then, the correlation between X and Y was continued to be analyzed by
using Spearman-Brown formula. The r
xy
was calculated as follows: �
�� =
� ∑ �� − ∑ �∑ � �{� ∑ −∑ �
2
}{ � ∑ �
2
−
�
2
∑ �
2
}
Notes:
r
xy
= Reliability coefficient N
= Total number of respondents ∑xy
= Total number of odd and even numbers ∑xy = Total number of odd items
∑y = Total number of even items
Sudijono, 1996:219 From the calculation, it was found that the reliability coefficient of a half
test was 0.43 for tryout of vocabulary post test. In order to find the reliability of the whole test the following calculation was done.
r
11
= 2r
xy
1 + r
xy
Notes: r
11
= reliability coefficient for the whole test items r
xy
= reliability coefficient for the half of the test items
From the calculation above, the reliability coefficient of the whole items of try out for vocabulary post test was 0.60. After calculating the reliability
coefficient of the whole items, the researcher gave the interpretation. If the range of the reliability coefficient of the whole items were from 0.60 up to 0.80
it meant that reliability coefficient of the whole items in the test was high. In other words,
the test was reliable. The calculation of the analysis of the reliability coefficient of the whole items of try out for vocabulary post can be seen on
Appendix K.
4.3 The Results of Primary Data
